This invention relates generally to fasteners, and more particularly concerns a threaded metal fastener which can be used in an outdoor environment, and which will provide a long service life without rusting or corroding.
Large, outdoor storage bins are ubiquitous in modern agriculture and industry. They have proved to be highly useful for storing large amounts of grains and foods to be consumed by poultry and other livestock. These bins are often assembled from curved panels which are bolted together. Bolts also secure the bin panels and other parts to legs and other support structure.
In many of these outdoor environments, the bolts can rust, and their stressed attachment to metal panels can cause accelerated rust and deterioration of the panels as well. Accordingly, it has been found helpful to provide bolts having heads which are entirely coated or jacketed in some way. To provide the desired protection from the environment, this molded jacket or coating covers not only over the upper surfaces of the head, but also extends under the bottom head clamping surface The jacket serves to protect the bolt head from rusting, and will also seal the workpiece aperture around the shank of the bolt
When assembling the bolts in the bin or other metal workpieces, the usual practice has been to hold the bolt head against rotation while tightening a nut on the bolt shank with an impact wrench. When installing standard, unjacketed, bare metal bolts, the impact wrench operator can hear a somewhat distinctive sound when the nut has been fully torqued or tightened into engagement with the bolt and workpiece. It is believed that this sound is at least partly provided by the metal contact between the bolt head clamping surface and the workpiece. However, completely jacketed bolt heads are insulated from the workpiece, and so there is no metal-to-metal contact, and no such distinctive sound is produced as the nut reaches its final position on the bolt shank. Consequently, the impact wrench operator cannot hear when full tightness has been obtained. Occasionally, then, bin assemblers over-tighten the bolts. This can result in extruding of plastic material out from beneath the bolt head bottom clamping surface. That extrusion may break the plastic sealing effect, and result in loss of corrosion resistance.
In addition, the plastic jacket layer located between the bottom bolt head clamping surface and the workpiece acts as a lubricant, which makes it much easier for the bolt head to turn relative to the workpiece. It is thus necessary to torque the nut upon the bolt shank with a greater than usual force, in order to obtain the desired amount of axial clamping pressure from the bolt.
Accordingly, it is the general object of the present invention to provide a metal fastener, such as a bolt, with a head having a plastic cover, but which can be attached to a workpiece with a head-metal-to-workpiece-metal contact.
It is another object to provide a bolt which co-operates with a torque wrench, nut and workpiece to provide a discernable sound when the bolt and nut have been properly torqued on the workpiece.
Another object is to provide a bolt having a completely jacketed head, which is so arranged that the plastic jacket is prevented from extruding from between the bolt head clamping surface and a workpiece when the bolt is attached to the workpiece.
Yet another object is to provide a bolt having a jacketed head which will withstand an installing torquing force of pre-designed magnitude during bolt installation or attachment to a workpiece.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings. Throughout the drawings, like reference numerals refer to like parts.